Re: Script to compute random page cost - Mailing list pgsql-hackers

From Curt Sampson
Subject Re: Script to compute random page cost
Date
Msg-id Pine.NEB.4.44.0209101153230.13186-100000@angelic.cynic.net
Whole thread Raw
In response to Re: Script to compute random page cost  (Tom Lane <tgl@sss.pgh.pa.us>)
Responses Re: Script to compute random page cost  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-hackers
On Mon, 9 Sep 2002, Tom Lane wrote:

> Finally, I wouldn't believe the results for a moment if they were taken
> against databases that are not several times the size of physical RAM
> on the test machine, with a total I/O volume also much more than
> physical RAM.  We are trying to measure the behavior when kernel
> caching is not helpful; if the database fits in RAM then you are just
> naturally going to get random_page_cost close to 1, because the kernel
> will avoid doing any I/O at all.

Um...yeah; another reason to use randread against a raw disk device.
(A little hard to use on linux systems, I bet, but works fine on
BSD systems.)

cjs
-- 
Curt Sampson  <cjs@cynic.net>   +81 90 7737 2974   http://www.netbsd.org   Don't you know, in this new Dark Age, we're
alllight.  --XTC
 



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